1. Field of Use
This invention relates generally to multisection telescopic booms such as used on mobile cranes and the like. In particular, it relates to a method of extending a jib section which is releasably mounted to the base of a boom, permitting relatively long boom extensions to be used.
2. Description of the Prior Art
Various types of multisection telescopic crane booms are known which have a base section, a second section with power means, an extension, and a jib detachably mounted on the base section. The detachable mounting of the jib to the base section enables the crane operator to readily attach the jib to the extension if needed, and leave the jib mounted to the base if the jib's additional length is not needed. In the stored position on current crane, a point at the other end of the extension is in vertical alignment with a point at the inner end of the jib. Before being pivotally attached to the extension at this point, the jib is typically attached to the extension thereabove at two other points, after which the extension and jib attached thereto must be pivoted around the end of the outermost telescoping section of the crane. An extension that would be as long as the base section along which it is stored would, in pivoting from its stored position to a position in which it may be used, be obstructed by machinery on the crane or by the crane operator's cab. Thus, the extension is made shorter than what would have been possible without such obstructions. In current cranes, the outer end of the extension goes no farther towards the rear of the crane than the inner end of the jib. As a result, several feet of potential stored extension length, rearward along the base section of the boom, are lost in current cranes of this type.